Exploring the engineered hierarchical MgO microspheres as a selective catalyst for the Claisen–Schmidt condensation reaction

Abstract

Exploring the utilization of earth-abundant metals for essential organic transformations is highly fascinating from an industrial viewpoint. In this present study, a simple and energy efficient precipitation protocol was employed for the synthesis of hierarchical MgO microspheres that were efficiently used as catalysts in the Claisen–Schmidt condensation reaction. The hierarchical MgO microsphere catalyst was prepared via a precipitation process using Na₂CO₃ as a precipitating agent under green reaction conditions. The inherent properties of the synthesized MgO hydroxide and MgO microspheres were well characterized using advanced analytical and spectroscopic techniques, such as TGA, XRD, FE-SEM, EDAX, TEM/HR-TEM, FT-IR, XPS, NH₃ and CO₂-TPD analyses. The synthesized MgO material successfully achieved excellent inherent properties, such as high thermal stability, good crystallinity, microsphere morphology, large specific surface area, and uniformly dispersed active sites on the material surface. Using the MgO catalyst, various reaction parameters, such as the effect of catalyst dosage, temperature, time, and solvents, were examined. As a result, chalcone was obtained as a product with 100% conversion and 90% yield in the presence of green solvent ethanol under reflux conditions at 80 °C for 20 h with 20 wt% catalyst amount. The catalytic activity was truly reliant on the inherent properties of hierarchical MgO microspheres. The competent MgO microsphere catalyst showed excellent catalytic activity for aldehyde and acetophenone molecules functionalized with electron-withdrawing groups and achieved respective chalcone products with excellent yields (84–91%) under optimized reaction conditions. The prominent structural and physicochemical properties facilitated catalytic activity in the Claisen–Schmidt condensation reaction under temperate reaction conditions. Remarkably, the efficient hierarchical MgO microsphere catalyst showed excellent recyclability up to 8 consecutive cycles with insignificant loss of its initial catalytic activity under optimized reaction conditions. The characteristic results of the spent MgO catalyst showed supportive evidence for stable structural and physicochemical properties.